This invention relates to a linear motor-actuated flow control valve assembly having an electromagnetically actuated and controlled moving-coil linear motor, and valve means for controlling the degree of communication between an inlet port and outlet port in accordance with the operation of the linear motor. More particularly, the invention relates to a valve assembly of the type described in which the flow rate between the two ports can be controlled in proportion to the electric current applied.
In general, a linear motor-actuated flow control valve of the aforementioned type includes a moving-coil linear motor which is arranged within a casing having an inlet port and an outlet port. The moving-coil linear motor comprises a hollow, ferromagnetic core which delimits valve chambers and which is provided with a valve hole for communicating the two ports, a bobbin, having an electromagnetic coil wound thereon, slidably disposed on the core for controlling the opening degree of the valve hole, permanent magnets so arranged as to produce a magnetic flux axially of the electromagnetic coil, and a ferromagnetic body for forming, together with the core, a magnetic circuit for the permanent magnets. The arrangement is such that passing an energizing current through the electromagnetic coil causes the bobbin to regulate the opening of the valve hole by moving the bobbin against a biasing force applied to the bobbin by spring means.
In the conventional linear-actuated flow control valve of the above kind, valve holes are disposed in a hollow ferromagnetic core (ordinally hollow iron core) forming a part of magnetic circuit for the permanent magnet. Namely both ports are communicated through valve holes which are circumferentially distributed at an angular distance along the periphery of the ferromagnetic core which is usually hollow and cylindrical. The opening degree of the valve holes is controlled by an end of the bobbin which is slidably disposed on the core. On one hand, the valve holes for controlling the flow rate should have such a given sectional area of the opening that a specific flow rate corresponding to a given electromagnetic force (namely the electric current) may be obtained, on the other hand it is required that the electromagnetic force should be correspondingly increased in order to obtain a given greater value of the opening degree of the valve holes. In spite of such requirements, there is a problem that a greater bobbin motive force can not be obtained owing to the saturation of magnetic flux caused by decrease in the sectional area of the magnetic circuit at the place where the valve holes are located even if a strong permanent magnet is used since the valve holes are disposed in the magnetic circuit. In other words, the increase in the sectional area of the opening of valve holes is apt to be contrary to the increase in the control electromagnetic force for increasing the opening of valve holes. This is a problem that it is difficult to design a valve assembly having a greater electromagnetic force.
This problem renders great obstruction to controlling the valve hole opening solely dependent upon the excitation current by presetting the control electromagnetic force with respect to a predetermined flow rate for the purpose of improving the control characteristics under application of shocks, namely preventing the valve from malfunction owing to shocks.
Furthermore, in a conventional arrangement of the valve holes the shape of valve holes is restricted based on that a given value of the sectional area of the magnetic circuit should be retained. Therefore, it is difficult to design any desired control characteristics since machining of two valve holes encounters difficulties depending upon the restriction in the shape of the valve holes.